1. Field of the Invention
The present invention relates to watercraft, and more particularly to a watercraft propeller propulsion system having a gimbal assembly with an external gimbal ring.
2. Description of the Related Art
Various types of propulsion systems are known for watercraft. The present disclosure relates to screw propeller propulsion units that mount to a transom of a boat and are often referred to as “surface piercing drives” or “surface drives”. Surface drive propeller propulsion systems are typically provided on boats which operate at high speed and usually have a partially submerged propeller with at least one degree of articulation for tilt or steering adjustment. Conventional surface drive propulsion systems for boats commonly have a rotating propeller shaft coupled via a rotating Universal joint (U-joint) to the drive shaft of a boat motor or engine. The drive shaft, propeller shaft and Universal joint are housed within a non-rotating housing with an articulation joint that allows the drive system to have at least one degree of articulation for tilt or steering adjustment. Various types of articulation joints are known, such as a gimbal. Some conventional configurations do not use a gimbal, but rather use a ball or hollow sphere fitted into a hemispherical seat. The present disclosure, however, is directed towards a gimbal or gimbal assembly.
It is noted that the gimbal, although similar in appearance to a Universal joint, has entirely different function, stress analysis, and design constraints such that it warrants a different art classification. A Universal joint is a device used to transmit rotary power in the form of torque from a first rotating shaft to a second rotating shaft at a high rate of speed in which one shaft is allowed to move through various angular deflections relative to the other shaft. A gimbal, on the other hand, is a non-rotating device that is often used to house a Universal joint contained within to provide a guide to the Universal joint and to transmit axial load as common with conventional propeller propulsion systems.
A gimbal assembly includes three main components including a first gimbal end, a gimbal ring, and a second gimbal end. The first gimbal end is hingedly connected to the gimbal ring by a pair of gimbal pins to allow articulation about a first axis. The second gimbal end is also connected to the gimbal ring by a second pair of gimbal pins to allow articulation about a second axis. One conventional gimbal assembly includes a gimbal ring that is internal to one gimbal end and that is external to the other gimbal end. Another configuration includes a gimbal ring that is internal to both gimbal ends. Conventional propulsion units use standard rolling element bearings pressed onto the propeller shaft and bolted into the propeller shaft housing and are difficult to access and remove and/or replace. Conventional drive systems do not have a means to measure propeller thrust forces.